Minerals play an important role in bulls as they function to form mucles of and maintain the quality of sperm. Zn mineral in the diet will also affect the levels of calcium and phosphorus in the blood. The objective of this study was to determine the effect of Zn supplementation on the levels of calcium and phosphate serum in Friesian Holstein bulls. This study used ten Friesian Holstein bulls, 16-18 months old and divided into two groups, consisting of five bulls each, i.e. with no added Zn (control) and 60 ppm of Zn supplementation, respectively. Zinc was administered daily for four months. Blood samples were taken before treatment and after the four- month treatment for the examination of calcium and phosphate levels. The result showed that 60 ppm Zn supplementation was not significantly different (p>0.05) on the blood calcium and phosphate levels. However, the calcium level tends to increase while that of phosphate tends to decrease.